An understanding is being sought of the mechanisms underlying visual acuity and visual hyperacuity. The latter is characterized by a spatial thereshold much smaller than the elements of the retinal mosaic. This kind of performance hence must have its basis in a neural processing mechanism by which small spatial differences are detected, probably at the expense of some other possible modes of information transformation. Experiments will be carried out on human observers to delineate their spatial and temporal differences detecting abilities, with such factors as exposure duration, adaptation, movement, binocularity and spatial features as parameters. Attempts will be made to identify test variables that allow the clinician to distinguish between various modes by which disease processes interfere with normal neural mechanisms of resolution and that will aid in the alleviation of resolution decrements by optical and other means.